Each Supreme Court justice has a single vote in deciding the cases argued before it; the chief justice's vote counts no more than that of any other justice. However, the chief justice—when in the majority—decides who writes the court's opinion. Otherwise, the senior justice in the majority assigns the writing of a decision. Furthermore, the chief justice leads the discussion of the case among the justices. The chief justice has certain administrative responsibilities that the other justices do not and is paid slightly more ($267,000 per year as of 2018, as opposed to $255,300 per year for each associate justice).[3]

Associate justices have seniority by order of appointment, although the chief justice is always considered to be the most senior. If two justices are appointed on the same day, the older is designated the senior justice of the two. Currently, the senior associate justice is Clarence Thomas. By tradition, when the justices are in conference deliberating the outcome of cases before the Supreme Court, the justices state their views in order of seniority. The senior associate justice is also tasked with carrying out the chief justices's duties when he is unable to, or if that office is vacant.[4] Historically, associate justices were styled "Mr. Justice" in court opinions and other writings. The title was shortened to "Justice" in 1980, a year before Sandra Day O'Connor became the first female justice.[5]

An associate justice who leaves the Supreme Court after attaining the age and meeting the service requirements prescribed by federal statute (28 U.S.C.§ 371) may retire rather than resign. After retirement, they keep their title, and by custom may also keep a set of chambers in the Supreme Court building, and employ law clerks. The names of retired associate justices continue to appear alongside those of the active justices in the bound volumes of Supreme Court decisions. Federal statute (28 U.S.C.§ 294) provides that retired Supreme Court justices may serve—if designated and assigned by the chief justice—on panels of the U.S. courts of appeals, or on the U.S. district courts. Retired justices are not, however, authorized to take part in the consideration or decision of any cases before the Supreme Court (unlike other retired federal judges who may be permitted do so in their former courts); neither are they known or designated as a "senior judge". When, after his retirement, William O. Douglas attempted to take a more active role than was customary, maintaining that it was his prerogative to do so because of his senior status, he was rebuffed by Chief Justice Warren Burger and admonished by the whole Court.[14]

There are three living retired associate justices at the present time: Sandra Day O'Connor, retired January 31, 2006; David Souter, retired June 29, 2009; and Anthony Kennedy, retired July 31, 2018. Both O'Connor and Souter occasionally serve on panels of the Courts of Appeals of various circuits. Kennedy has not performed any judicial duties.

^The start date given here for each associate justice is the day they took the oath of office, and the end date is the day of the justice's death, resignation, or retirement.

^Listed here (unless otherwise noted) is the position—either with a U.S. state or the federal government, or with a private corporation—held by the individual immediately prior to becoming an Associate Justice of the Supreme Court.